1. Field of the Invention
This invention relates to a unique group of catalysts of remarkable activity for the polymerization of 1-olefins and to an improved process for the polymerization of olefins to provide linear polymers and copolymers, said process employing the improved catalyst system comprising a Group IV(a) transition metal hydrocarbyl hydride aluminate bonded to the surfaces of alumina for use therein, and to the process for production of the improved catalyst. More specifically, this invention relates to a process for the homopolymerization and copolymerization of ethylene, propylene, butene-1 and higher 1-olefins in which the catalyst system is the product obtained by the reaction of a tetra(hydrocarbyl) transition metal compound, (R--CH.sub.2 --.sub.4 M, where M is Ti, Zr or Hf and R-- is an aryl, aralkyl or tertiary alkyl group which contains no H-radical attached to the carbon atom in the .beta.-position to the metal, M, with a partially hydrated alumina followed by hydrogenation of the adduct to a preselected degree prior to injection into a polymerization zone where the catalyst, usually suspended in an inert hydrocarbon medium, is contacted with the olefin or olefins to be polymerized.
2. Prior Art
In 1954 and 1955 pioneering advances in olefin polymerization catalysts were disclosed by Karl Ziegler and associates at the Max-Planck Institute for Coal Research in Mulheim, Germany, and by Arthur Anderson and associates in the laboratories of E. I. du Pont de Nemours and Company in Wilmington, Delaware. These new catalyst systems, now frequently termed coordination catalysts, were based on transition metal salts (e.g. titanium, zirconium or vanadium halides) which had been converted into reduced valence states by reaction with a variety of alkylating or arylating substances, usually simple organometallic compounds of a metal of Groups, I, II or III of the Periodic Table of Elements (the Bohr long form). It is believed that the mechanism of catalyst production involves alkylation (or arylation) of the transition metal halide followed by rapid decomposition of the unstable, transitory transition metal-alkyl (or aryl) compounds to give more stable complex products of lower valency which actively coordinate with and polymerize olefins by a coordination-polymerization mechanism. Unlike the commercial polyethylene or any polypropylene previously known prepared by free-radical or ionic catalysts, polyolefins prepared with coordination catalysts are of very high molecular weight and linear and highly ordered, thus exhibiting, in the case of homopolymers, such a high degree of chemical structural regularity and linearity that they are highly crystalline and exhibit high crystalline melting points, making them extremely valuable as textile fibers, films, and molded articles of commerce. Generally, however, it has been necessary in the case of these coordination catalysts to devise processes to remove the catalyst residues, which comprised the transition metal halides, since the residues were present at such levels as to discolor the polymer and the halide was too corrosive in subsequent fabrication machinery.
More recently some more stable organometallic transition metal complexes, usually including a halide anionic ligand or a neutral Lewis Base ligand, have been disclosed in patents of Gunther Wilke of the Max-Planck Institute and in patents of several researchers in the laboratories of I.C.I. in England, and in several patents of researchers in the laboratories of Hercules, Inc. in the United States.
Illustrative of the Wilke patents are U.S. Pat. Nos. 3,379,706, 3,424,777, 3,432,530, 3,540,728, 3,468,921 and 3,536,740. In all of these Wilke patents the hydrocarbyl groups attached to a transition metal are members of the class of .pi.-allylic compounds characterized by the structure ##EQU1## in which the R-radicals may be H-- or any alkyl, aryl or aralkyl radicals or R.sub.1 and R.sub.4 may together form a ring comprising methylene groups. Interactions between the .pi. electrons and the electrons of the transition metal presumably occur affecting the stability and chemical reactivity of the complexes. The bonding of these .pi.-allyl radicals to the transition metal is more stable than in the case of sigma-bonded n-alkyl groups but less stable than for the hydrocarbyl groups employed in the catalysts of the present invention which have no H-radicals attached to the C-atom beta to the metal. These metal-.pi.-allyl compounds are reacted with Lewis acids, such as HX, where X is halide, or Lewis Bases, such as tertiary amines or phosphines, to form complexes showing activity as olefin oligomerization or polymerization initiators. However, polymerization reactions using such initiators generally must be conducted as slurry polymerizations at low temperatures, because of marginal thermal stability and low solubility of the .pi.-allyl complexes, and have been found less than fully satisfactory in the yields and molecular weight of polymers produced. Furthermore, because of their corrosive and often toxic nature, the catalyst residues must be removed from the polymeric products by time-consuming and costly procedures in order to provide products of general utility and safety in commerce.
One improvement on the use of these .pi.-allylic transition metal complex catalysts in olefin polymerization is disclosed in U.S. Pat. No. 3,732,198 of Whitely et al., assignors to I.C.I., who disclose the polymerization of ethylene with a combination of a classical coordination catalyst with a transition metal complex of a .pi.-allylic compound.
The patents arising from the work of researchers at I.C.I. in England are illustrated by U.S. Pat. Nos. 3,681,317, 3,740,384, 3,738,944 and British Pat. No. 1,314,828. All of these involve tetrabenzyl-transition metal compounds (e.g. tetrabenzyl zirconium) complexed with anionic ligands (e.g. halide) and/or neutral ligands (e.g. pyridine) as ethylene polymerization catalysts. In certain cases there are disclosed as ethylene polymerization catalysts the reaction products of tetrabenzyl-zirconium compounds with inorganic oxides free of absorbed water but containing surface HO-- groups. Reasonable thermal stability is achieved with these substances. They apparently yield high molecular weight polyethylene but the polymerization rate and efficiency and polymer yield obtained with those catalysts in processes operating at short hold-up times and temperatures below 150.degree.-200.degree.C. for the polymerization of ethylene are not as high as with the catalysts of this invention.
Illustrative of the patents assigned to Hercules, Inc. are Kruse, U.S. Pat. No. 3,773,742, disclosing tetraneopentyl titanium as an ingredient in an olefin polymerization catalyst, either alone or in combination with an organoaluminum compound or supported on an annealed, microspheroidal silica gel, and Kruse, U.S. Pat. No. 3,798,250, disclosing tetrahydrocarbyl chromium compounds, such as tetra(neopentyl) chromium and tetra(neophyl)chromium, as olefin polymerization catalysts either in solution or extended on a solid silica support.